Optical alignment on vacuum plenum

ABSTRACT

An arrangement of a planar positioning means in an electrostatic printing machine of the type employing a flexible photoconductive member, such as a belt or web. The machine is provided with locating pins in the image plane for the machine and against these pins, a vacuum holddown device is yieldably maintained. The belt or web is held against the holddown device during movement of the belt or web thereby being continuously held within the image plane. Means are provided for the movement of some of the locating devices for permitting removal or insertion of the belt or web without danger thereto.

Elite States Patent [191 Jordan Jan. 14, 1975 [54] OPTICAL ALIGNMENT ONVACUUM 3,521,950 7/1970 Gardner et al 355/3 PLENUM llsllagle ason e a.[75] Inventor: William E. Jordan, Penfield, NY 3,592,404 7 1971 Ncrwin95 31 CA x Assigneet Xerox Corporation, Stamford 3,665,829 5/1972Putscher 95/31 CA Conn Primary Examiner-Samuel S. Matthews [22] Filed:Jan. 29, 1973 Assistant Examiner-Kenneth C. Hutchison [21] Appl. No.:327,378 57 ABSTRACT Related US Application Data \n arrangement of aplanar positioning means in an [63] gg i g of June 1971 electrostaticprinting machine of the type employing a flexible photoconductivemember, such as a belt or U S Cl 355/16 271/74 354/203 web. The machineis provided with locating pins in the 355/73 image plane for the machineand against these pins, a Int Cl G03 15/00 vacuum holddown device isyieldably maintained. The [58] Fie'ld g belt or web is held against theholddown device during CA i i Rf354/2O3 movement of the belt or webthereby being continuously held within the image plane. Means areprovided [56] References Cited for the movement of some of the locatingdevices for UNITED STATES PATENTS permitting removal or insertion of thebelt or web without danger thereto. 3,490,84l 1/1970 Cel et al 355/3 R3,506,348 4 1970 Broi lie 2 Clam, 8 Drawmg PATENTED 1 M975 3 860 340 sum1 [1F 6 INVENTORS WILLIAM E. JORDAN ATTORNEY F/GI PATENTED JAM M975SHEET 2 BF 6 PATENTED JAN 1 4 SHEET 3 BF 6 PATENTEB JAN 1 4 I975 sum 6or e m mt OPTICAL ALIGNMENT ON VACUUM PLENUM This is a continuation ofapplication Ser. No. 151,406, filed June 9, 1971, now abandoned.

This invention relates to electrostatic printing machines, and inparticular, to a unique configuration of means associated with aflexible photoreceptor belt or web for insuring optical alignment of thebelt or web at the exposure station for the machine during installationof the belt.

Electrostatic printing machines of the endless belt type employ anexposure station positioned so that the belt is continously carriedtherethrough during machine operation. In the configuration of thesemachines, provision is had for the removal or installation of a belt andgenerally this provision will be in the form of a belt assembly modulewhich may be mounted in the machine for easy removal as a unit. Duringsuch movement of the belt, care must be taken to prevent inadvertentcontact of the belt with parts of the machine. This same care must betaken as the unit with the belt mounted thereon is moved back intooperating position. When the belt is returned to the machine, it isimportant that the belt run which is to be in coincidence with theexposure station be returned precisely in its former position, beforeremoval.

Therefore, the pincipal object of the present invention is to improveelectrostatic printing machines of the type employing electrostaticphotoreceptor belts or webs.

Another object of the present invention is to protect a photoreceptorbelt during movement thereof against inadvertent contact with extraneousstructure and to insure the repositioning of a run thereof incoincidence with the exposure station.

The foregoing objects are attained by an arrangement of a vacuum plenumon the side of an endless electrostatic photoreceptor belt opposite thatwhere a light image pattern is projected and which defines the imageplane for an original to be reproduced. The vacuum plenum is in the formof a generally rectangle flat hollow structure having the interiorconnected to a vacuum producer. The belt is drawn against one flat sideof this plenum in order to maintain the belt flat during exposure of thebelt to imaging light rays of an original to be copied. The machineframe is provided with a plurality of locating pins which define a planein coincidence with the exposure plane or the image plane of the opticalsystem for the machine. The plenum is arranged to be movable away andtoward these locating pins and to contact the same for positioning therun of the belt on the plenum in the image plane.

Further objects and advantages will become apparent after reading thefollowing specification in conjunction with the accompanying drawingswherein:

FIG. 1 is a schematic sectional view of an electrostatic reproductionmachine embodying the principles of the invention;

FIG. 2 is a partial cross-sectional view of a belt assembly as seen fromthe front of the machine;

FIG. 3 is a plan view, partly broken away of a vacuum holddown device;

FIG.. 4 is a sectional view taken along lines 4-4 in FIG. 3 showing theholddown device in an inoperative condition;

FIG. 5 is a view similar to that in FIG. 4 but showing another conditionof operation;

FIG. 6 is an isometric schematic view of the optical system of themachine as applied to a photoreceptor belt;

FIG. 7 is an enlarged sectional view of the exposure station and vacuumholddown device when the belt assembly is in its operating position inthe machine; and

FIG. 8 is a sectional view of the exposure station from a directionabove the machine.

For a general understanding of the illustrated copier/reproductionmachine, in which the invention may be incorporated, reference is had toFIG. I in which the various system components for the machine areschematically illustrated. As in all electrostatic systems such as axerographic machine of the type illustrated, a light image of a documentto be reproduced is projected onto the sensitized surface of axerographic plate to form an electrostatic latent image thereon.Thereafter, the latent image is developed with an oppositely chargeddeveloping material to form a xerographic powder image, corresponding tothe latent image on the plate surface. The powder image is thenelectrostatically transferred to a support surface to which it may befused by a fusing device whereby the powder image is caused permanentlyto adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon atransparent support platen P fixedly arranged in an illuminationassembly generally indicated by the reference numeral 10, arranged atthe left end of the machine. While upon the platen, an illuminationsystem flashes light rays upon the original thereby producing image rayscorresponding to the informational areas on the original. The image raysare projected by means of an optical system for exposing thephotosensitive surface of a xerographic plate in the form of a flexiblephotoconductive belt 12 arranged on a belt assembly generally indicatedby the reference numeral 14.

The photoconductive belt assembly 14 is slidably mounted upon twosupport shafts one of which is secured to the frame of the machine andis adapted to drive a belt 12 in the direction of the arrow at aconstant rate. During this movement of the belt, the reflected lightimage of an original on the platen is flashed upon the photoreceptorsurface of the belt to produce electrostatic latent images thereon at anexposure station A.

As the belt surface continues its movement, the electrostatic imagepasses through a developing station B in which there is positioned adeveloper assembly generally indicated by the reference numberal l5, andwhich provides development of the electrostatic image by means ofmultiple magnetic brushes as the same moves through the developmentzone.

The developed electrostatic image is transported by the belt to atransfer station C whereat a sheet of copy paper is moved between atransfer roller and the belt at a speed in synchronism with the movingbelt in order to accomplish transfer of the developed image solely by anelectrical bias on the transfer roller. There is provided at thisstation a sheet transport mechanism generally indicated at 17 adapted totransport sheets of paper from a paper handling mechanism generallyindicated by the reference numeral 16 to the developed image on the beltat the station C.

After the sheet is stripped from the belt 12, it is conveyed into afuser assembly generally indicated by the reference numeral 18.whereinthe developed and transferred xerographiepowder image on the sheetmaterial is permanently affixed thereto. After fusing, the finished copyis discharged from the apparatus at a suitable point for collectionexternally of the apparatus.

The belt 12 comprises a photoconductive layer of selenium which is thelight receiving surface and imaging medium for the apparatus, on aconductive backing. The belt is journaled for continuous movement uponthree rollers 20, 21 and 22 located with parallel axes at approximatelythe apex of a triangle. During exposure of the belt 12, the portionthereof being exposed is that part of the belt run between the rollerand the lower roller 21. The upper roller 22 is rotatably supported on ahollow shaft 23 which is rotatably driven by a suitable motor and drive(not shown) mounted in the machine. Further details regarding thestructure of the belt assembly l4 and its relationship with the machineand support therefor may be found in the copending application Ser. No.102,312, now US. Pat. No. 3,730,623, assigned to the same assignee. Fromthe copending application, it will be understood that the belt assembly14 is mounted in cantilever fashion on the frame of the machine by meansof the hollow shaft 23 and another hollow shaft 24, and that the beltassembly is adapted to be accurately positioned inits required locationafter movement of the assembly from the machine frame. It will beappreciated that this structure allows easy removal and replacement ofthe belt assembly upon the frame while still providing means for drivingthe belt and permit removal of the belt 12 from its supporting assembly.

As shown in FIG. 2, the belt assembly is in a form which provides threebelt runs; that is, sections of the belt that lie in flat planes. Inorder to provide an exposure run which is truly flat and which insuresthe positioning of a belt run in a precisely located plane, free ofvibration, inadvertent deflection and which will assume the workingposition at all times, the belt assembly is provided with a flatholddown device for the exposure run. To this end, the exposure beltrun, that is, the run between the rollers 20, 21 has associatedtherewith a holddown device 50.

As shown in FIG. 3, the vacuum holddown device 50 comprises a vacuumplenum 51 having a flat surface plate 52 formed therethrough with manyopenings 53 upon which the photoconductive belt 12 is stretched acrossduring movement thereof. On the other side of the plate away from thebelt 12, the plenum includes a plurality of ribs 54 made integral withthe plate 52 and projecting from the surface thereof. Along with theribs, there is also integrally formed on the same side of the plate 52,a circumferential guard wall 55 which is connected to the exterior endsof all the ribs 54 and also which surrounds all of the openings 53.

The spaces between the ribs 54 and the circumferential wall 55 areclosed off on that side of the plate 52 by a manifold 56 made offlexible plastic material and having a relatively flat web portion 57positioned to span across all of the ribs and the wall 55. The outercircumference edge of the manifold 56 is formed with a wall 58 whichextends toward the plate 52 and completely surrounds the wall 55. Thewall 58 terminates in a flange 59 which is secured to the adjacentsurface of the plate 52 by suitable lock washers 60. In order to insurea vacuum seal within the interior chamber defined by the flat portion 57of the manifold 56 and the plate 52, a circumferential gasket 61 orsealing device is positioned between the flange 59 and the plate. Themanifold 56 also includes a chamber 62 formed with material from the webportion 57 and which terminates in a hose connector 63 to which a hoseof an air evacuation system may be secured. The chamber walls 62 extendbeyond the plane of the web portion 57 approximately centrally of theplate 52 in order to provide access to all of the spaces between theribs 54. As shown in FIG. 3, the chamber is in communication with all ofthe spaces between all of the ribs 54 some of which terminate short ofthe central coresection 64 of the vertical and horizontal ribs as viewedin this figure.

In order to extend the vacuum effectiveness of the holddown device 50,the plate 52 on the side supporting the belt 12 is formed with grooves65 of semi circular cross-section connected to some of the outermostseries of opening 53 and terminating adjacent the outer opposed edge ofthe plate 52. Since air is evacuated out of the space defined by thecircumferential wall 55 within which the outermost series of openings 53are confined, the effect of the vacuum produced by this evacuation ofair will be felt at the extreme outer limits of the grooves 65 and alongthe same. With the belt applied to the outer surface of the plenum plate52 as shown in FIG. 4, and with the plenum subjected to a vacuumproducing system, the belt will be forced against the plate by theresultant pressure differential effected between the spaces on eitherside of the plate 52. The effect of this force on the belt will extendbetween the outer ends of the series of grooves 65 on one edge of theplate 52 to the outer ends of the series of grooves at the other edge ofthis plate.

This force on the belt will be continuous as the same moves on the beltassembly 14 and will produce a flattened, unwavering portion of the beltfor the exposure step in the utilization of the machine. The vacuumholddown device 50 located in the exposure zone A will fix the beltduring movement relative to the conjugate of the optical axis for theprinting machine which will be described in detail hereinafter.

The vacuum holddown device 50 also is provided with a flexible webmaterial 66 stretched across the plenum plate 52 for various purposes.The web material 66 is electrically insulating since the surface of thebelt 12 which slides across the material and which is under considerablyforce thereon, comprises the conductive layer of the photoconductivebelt. The material 66 then electrically insulates the belt 12 relativeto the holddown device. In addition, the material, preferably made ofsoft fabric or paper, protects the conductive layer of the belt againstabrasions and wear, as well as to reduce the friction between the movingbelt and the plate 52 and to prevent the plugging or restricting of theopening 53 by dirt, etc. The web 66 is maintained on the outer surfaceof the plenum plate 52 by means of a pair of parallel arranged rods 67,68 secured to each end of the material and held in fixed positions underthe outer edges of the plenum plate. Further details of the web and itsmounting are disclosed in the above-referred to copending patentapplication.

During machine shutdown when a vacuum producing means, which isgenerally in the form of a blower and duct work, in the printing machineis inoperative, the web 57 for the manifold 56 is in its flattened,unstressed condition as shown in FIG. 4. When the vaccum producing meansis rendered operative, air is drawn from the external circuitry of theplenum 51 through the material 66 and openings 53 through the spacesbetween the ribs 54 and within the wall 55 and out of the chamber 62.With the belt 12 being applied against the plenum 51, a vacuum isproduced in these spaces to cause the belt to be drawn under force uponthe plate 52 and also to cause the web 57 to flex and be drawn againstthe adjacent edges of the ribs 54, as shown in FIG. 5. Normally, whennot so flexed, the web 57 is spaced slightly from these edges of theribs thereby maintaining the manifold 56 and the plenum 51 in unstressedcondition. However, under vacuum conditions, which would cause thetendency for the plenum plate to flex, an undesirable result, theflexing of the web 57 and the forces produced by the vacuum conditionsthereon and what these resultant forces will produce, in turn, upon theribs 54, eliminates actual flexing of the plate 51.

In order to insure positioning of the plane of the exposure run incoincidence with the image plane of the imaging system for the machineand thereby assure proper focusing of an object upon the image plane, orwithin the focal range of the optical system for the machine, locatingmeans are provided on the portion of the machine frame which supportsthe optical system therefor. The locating means cooperates with thevacuum holddown means 50 for this positioning, and both the locatingmeans and the holddown means are adapted to permit the easy removal ofthe belt assembly supporting the belt and its repositioning in themachine with the exposure belt run returned to is former position forimaging purposes.

As shown in FIG. 6, the optical system for the machine includes theglass platen P upon which an original to-be-reproduced is placed, amirror 72 which directs imaging light rays from the original, aprojection lens system 71 into which the light rays from the mirror 72are received, and a second mirror 72, which directs the light raysprojected from the lens 71 to an image plane represented in FIG. 6 byfour little crosses and indicated by the reference numeral 75. Theworking conjugate distances for the projection lens 71 extend betweenthe center plane of the platen P to the center of the image plane 75, asfolded by the mirrors 70, 72 and extending through the lens 71. With anapproximate 11] magnification ratio for the lens, the distances betweenthe same and the object plane and the image plane are approximatelyequal.

Also, in the image plane 75 are a plurality of locating pins mounted onthe frame 76 supporting the optical system and having their contactingtips precisely held in this plane. Two of these pins 77, 78 arepositioned inwardly of the machine frame generally along and parallel tothe adjacent side of the image plane 75. At the outward side of theimage plane, or that side closest to the viewer when viewing the machineas oriented in FIG. 1, two additional pins 80, 81 are mounted therebyestablishing four contact points within the image plane. As shown inFIG. 7, the inwardly positioned pins 77, 78 are fixed by means ofbrackets 83 to the machine frame 76. Each of the pins 77, 78 ispreferably formed with threaded shafts and are treadedly received intheir respective brackets. Suitable lock nuts 84 are provided forsecuring each pin when each has been adjusted in order to place theircontact tips 85 precisely at the image plane 75 of the machine opticalsystem.

The pins 77, 78 are opposite the plenum 51 and adapted to engage theplate 52 when the belt assembly 14 is in operating position in themachine.

In order to provide an override supporting connection, to insure properpostioning of the belt contacting surface of the plate 52 relative tothe image plane, and to prevent damage to either the pins or the plate52, the holddown device 50 is yieldably mounted on its supportingstructure in the belt assembly by means of three coil springs 86. One ofthe springs is positioned adjacent the forward edge of the plate 52 andthe two, one at each corner of the rearward edge of the plate, with allthree being located on the side thereof away from the photoreceptor belt12. Each yieldable connection is formed by a threaded shank 87 securedto the frame of the belt assembly 14, the spring 86 encircling a shankand secured at one end to the adjacent portion of the frame, andengageable with the opposite portion of the plate 52. These oppositeportions may be formed with suitable openings 88 (see FIG. 3) to receivethe shank. With each of three spaced points of the plenum plate 52supported in this way, it will be obvious that the holddown device iscapable of floating in its mounting and to assume a limited planarorientation depending upon external contacts.

As previously stated the rearward edge of the plate 52 contacts therearward located fixed pins 77, 78. The pair of locating pins 80, 81 arealso positioned for coaction with the plenum plate 52 along its forwardedge. With pins 80, 81 in operating position as shown in FIGS. 6, 7 and8, the plenum plate 52 is properly oriented so as to place the exposurerun of the photoreceptor belt 12 on exact coincidence with the imageplane of the optical system. In order to permit movement of the beltassembly 14 from its working position, the pins 80, 81 are mounted in alocking device which aids in holding the belt assembly in its workingposition and which is adapted to be released in a step preparatory tomovement of the assembly.

The pins 80, 81 are positioned in a vertical plane and are adjustablysecured in a plate 92 formed integrally with a lever 93. One end 94 ofthe lever is in the form of a handle and its other end is pivotallysupported by a bracket 95 secured to the machine frame, designated bythe numeral 76. The bracket 95 includes a bifurcated end 97 to which thelever 93 is pivotally retained by means of a pivot pin 98.

Each pair of the pins 77, 78 and 80, 81 is adapted to cooperate with abearing surface 100 and 101 respectively, formed in the correspondingedges of the plenum plate 52 at a slight incline angle so that thecorresponding pin may slide. When the belt assembly is to be moved outof its working position, or from the position shown in FIG. 6 to theright, the initial movement causes the inclined bearing surfaces 100 toslide laterally relative to the pins 77, 78 until the edge of the plate52 is clear. In this action, the plate 52 also is forced slightlyoutwardly by the springs 86. Before this movement of the belt assembly,however, the pins 80, 81 would have been removed out of contact withcoacting bearing surfaces 101 by activating the handle 94 in a clockwisedirection, as viewed in FIG. 8, about the pivot 98. As was the case forthe rearward positioned springs 86 upon the plenum 51, the singleoutward spring 86 will force the adjacent edge of the plenum outwardlyas the pins 80, 81 are so moved. With the pins 80, 81 out of its lockingposition, the belt assembly may be moved out of the machine withoutdanger of any of the pins 77,78 and 80, 81 coming in contact with thephotoreceptor belt.

In returning the belt assembly to its working position, which will be inthe focal range of the optical system, the last increment of movementwill cause the pins 77, 78 to contact the inclined portions 103 of thebearing surfaces 100 and ride up the same in a manner which forces thisend of the plenum slightly further into the belt assembly against thebias of the two springs 86. With the belt assembly in its workingposition, the handle 94 is rotated so as to effect the contact of thepins 80, 81 upon the inclined portions 104 of the bearing surfaces 101.As the pins ride up this surface, the adjacent end of the plenum willalso move inwardly against the bias of the single spring until the pinsassume their locked position as shown in FIG. 8. The belt assembly isnow in a locked position and the belt 12, which moved slightly inwardlywith the plenum plate 52, will assume again the plane in the focal rangeof the optical system.

While the invention has been described with reference to the endlessbelt structure for the form of photoreceptor, it will be understood thatthe invention may be applicable to web structure in an arrangementhaving a supply roller with either a take-up roller or sheetcuttingstructure. In addition, other devices may be utilized by producing aplanar exposure run, such as belt tensioning means, either added to thebelt assembly or associated with one of the rollers supporting the belt,or by directing the belt or web in such a way as to utilize gravity toassist in defining a planar course. It is in tended to cover suchmodifications or changes as may come within the scope of the followingclaims.

What is claimed is:

1. An electrostatic printing machine having an exposure station, and animaging system which includes an image plane, the machine comprising:

an assembly comprising a plurality of rollers movably mounted forsupporting and guiding a flexible photoreceptor member around therollers to effect an exposure run at the exposure station when theassembly is in its working position;

a holddown device comprising a plenum plate, the

plenum plate defining a planar surface against which the photoreceptormember is held for maintaining the surface of the latter in asubstantially planar condition at the exposure station, the

t plenum plate being mounted for limited movement in a directionsubstantially perpendicular to the image plane;

a plurality of locating devices defining the image plane in coincidencewith the exposure station, the holddown device including means adaptedto engage the locating devices for maintaining the surface of thephotoreceptor member in the image plane during movement of thephotoreceptor member;

biasing means adatped to urge the holddown device against said locatingdevices to maintain the sur face of the photoreceptor member in theimage plane;

means permitting the assembly to be moved into and out of its workingposition in a direction transverse to the direction in which thephotoreceptor member moves around the rollers without any of thelocating devices contacting the photoreceptor member;

wherein the plenum plate has a forward and a rearward edge, wherein theengaging means comprises a plurality of bearing surfaces formed in theforward and rearward edges of the plenum plate, the bearing surfaces inthe rearward edge each having an inclined portion arranged thereon sothat the locating devices associated therewith will slide over thesurface as the assembly is moved into its working position, and whereinthe locating devices associated with the bearing surfaces on the forwardedge are movable mounted so that the locating devices can be moved intoand out of contact with their associated bearing surfaces so as topermit the assembly to be locked into and unlocked from its workingposition.

2. An electrostatic printing machine as set forth in claim 1, whereinthe bearing surfaces on the forward edge each have an inclined portionarranged thereon so that the locating devices associated therewith willslide over the surfaces as the locating devices are moved into and outof contact with the bearing surface. a

1. An electrostatic printing machine having an exposure station, and Animaging system which includes an image plane, the machine comprising: anassembly comprising a plurality of rollers movably mounted forsupporting and guiding a flexible photoreceptor member around therollers to effect an exposure run at the exposure station when theassembly is in its working position; a holddown device comprising aplenum plate, the plenum plate defining a planar surface against whichthe photoreceptor member is held for maintaining the surface of thelatter in a substantially planar condition at the exposure station, theplenum plate being mounted for limited movement in a directionsubstantially perpendicular to the image plane; a plurality of locatingdevices defining the image plane in coincidence with the exposurestation, the holddown device including means adapted to engage thelocating devices for maintaining the surface of the photoreceptor memberin the image plane during movement of the photoreceptor member; biasingmeans adatped to urge the holddown device against said locating devicesto maintain the surface of the photoreceptor member in the image plane;means permitting the assembly to be moved into and out of its workingposition in a direction transverse to the direction in which thephotoreceptor member moves around the rollers without any of thelocating devices contacting the photoreceptor member; wherein the plenumplate has a forward and a rearward edge, wherein the engaging meanscomprises a plurality of bearing surfaces formed in the forward andrearward edges of the plenum plate, the bearing surfaces in the rearwardedge each having an inclined portion arranged thereon so that thelocating devices associated therewith will slide over the surface as theassembly is moved into its working position, and wherein the locatingdevices associated with the bearing surfaces on the forward edge aremovable mounted so that the locating devices can be moved into and outof contact with their associated bearing surfaces so as to permit theassembly to be locked into and unlocked from its working position.
 2. Anelectrostatic printing machine as set forth in claim 1, wherein thebearing surfaces on the forward edge each have an inclined portionarranged thereon so that the locating devices associated therewith willslide over the surfaces as the locating devices are moved into and outof contact with the bearing surface.